Technician Todd Boman collects soil electrical conductivity
readings as he drives through a vegetative treatment area. These values
are used to generate maps illustrating nutrient distribution in the
vegetative treatment area.

The same precision farming techniques that work with crops can work
with manure management on cattle feedlots.

Agricultural engineers Roger Eigenberg and Bryan Woodbury and
colleagues at the Agricultural Research Service Environmental Management
Research Unit at the Roman L. Hruska U.S. Meat Animal Research Center in
Clay Center, Nebraska, map the distribution of manure on the surface of
feedlots and the flow of liquid manure in rain runoff.

This research could lead to both precision harvesting of manure and
precision application of manure to crop fields, while controlling
nutrient losses and gas emissions.

The scientists map manure distribution by towing a GPS-equipped
sensor on a trailer pulled by an all-terrain vehicle over feedlot pens
and cropland at about 6 miles per hour. The sensor estimates the amount
and quality of manure in various places on the feedlot surface by
measuring the manure's ability to conduct electricity.

Manure contains about 5 to 10 percent salt by dry weight, which
comes from salt supplements in cattle feed. Salt in solution is an
excellent conductor of electricity; therefore, dissolved salt in manure
and manure-amended soils increases their electrical conductivity.

Eigenberg, Woodbury, and colleagues used a computer program called
"ESAP," for Electrical Conductivity Spatial Analysis Program,
to choose spots on the feed lots and a nearby hayfield to sample soils,
rather than sample randomly. The U.S. Salinity Laboratory in Riverside,
California, developed the program. Eigenberg and colleagues used the
program to associate high soil conductivity levels with manure solids
and with the chloride in the salts found in manure.

In more recent work, Woodbury, Eigenberg, and colleagues found that
they could also use the program to correlate high soil conductivity with
nitrogen, phosphorus, and the volatile fatty acids associated with
manure odors.

In the earlier study, Eigenberg and Woodbury compared two
experimental beef cattle feedlot pens at Clay Center--each having a very
different, but common, management style--and found the correlations
worked well in estimating the quantity and quality of manure solids on
the feedlot floor in both pens.

The soil conductivity and modeling techniques could be used to help
feedlot operators recover valuable byproducts from the feedlot. For
example, manure with higher nitrogen and phosphorus content could be
harvested for use as fertilizer. This would have the added benefit of
reducing nutrient losses, and it could identify areas prone to odors so
they could be treated with improved drainage or, possibly, with
antimicrobial compounds.

Eigenberg and Woodbury also mapped a vegetative treatment area
downslope of the Clay Center feedlot. Rain runoff from eight pens flows
into a settling basin at the base of the feedlot. After the solids
settle, the liquid manure flows through tubes onto a hayfield designed
to capture and use manure nutrients.

The scientists could tell from the soil conductivity maps that the
liquid manure was being unequally distributed. With this information,
they made adjustments to the flow tubes, resulting in a more uniform
distribution of the runoff and improved effectiveness of the treatment
area.

"The idea is to have more of the nitrogen and phosphorus
fertilizing hay than being lost to the environment," Eigenberg
says. "This work will help improve techniques for handling manure
on both feedlots and crop fields. Manure can be harvested for the
greatest value possible, whether for energy or fertilizer, and used more
efficiently, which should greatly reduce pollution and odors."--By
Don Comis, ARS.

This research is part of Agricultural and Industrial Byproducts
(#214), an ARS national program described at www.nps. ars.usda.gov.